This investigation deals with the systematic study and definition of the performance and efficiency characteristics of the stable hypertrophied myocardium in vivo, its metabolic aspects and interaction with the rest of the circulation, and the transition between stable hypertrophy and failure. We have developed a model of stable left ventricular hypertrophy in dogs, rabbits and rats, to study the various aspects mentioned above as they pertain to the selectively hypertrophied left ventricular chamber. The studies so far indicate that the stable hypertrophied myocardium performs in a similar fashion to the normal myocardium and is no less efficient. It responds to stress in a similar way as normal heart. However, resting coronary blood flow per unit myocardial mass is decreased, and oxygen extraction at rest is increased. Extraction is not increased with stress as in the normal myocardium, and the increased oxygen requirements under stress are met by increased coronary blood flow. Regional distribution of blood flow in the hypertrophied myocardium is similar to that in normal, as is the concentration of energy-yielding compounds. The continuing thrust of the investigation in the coming grant period is aimed at the definition of the effect of added insults such as ischemia, hypoxia, shock, chronic volume overloading, and the performance characteristics of the stable hypertrophied myocardium. Studies are aimed at better understanding of the physiology and biochemical alterations in stable hypertrophy in order to better define the optimal timing and the role of corrective surgery for lesions which are accompanied by a rather long stage of stable hypertrophy.